Understanding AHS Chart Symbology

At first glance, an Australian Hydrographical Survey (AHS) chart looks simple to interpret, however, what exactly do all those different symbols mean? Before your next day on the water, have a look at the symbols taken from a few Australian nautical charts.

On this page, you may be able to notice how, on the left, the depth contours are dashed and the depth values (soundings) are written in upright text. This means they are from older or incomplete surveys.

In contrast, in the shipping route on the right, the depth contours are unbroken and the soundings are written in sloped italic text. This means they are from modern and more reliable surveys. More information can be found in the AHS Fact Sheet – Accuracy and Reliability of Charts.

On the next two pages a wide variety of chart symbology, plus simple explanations for each, should help next time you venture into unfamiliar areas.